Research And Implementation Of Low Phase Noise Frequency Synthesizer

With the advance of science and technology, the electronic test and measurement system also Rapid development such as the space communication, 3 g communication, satellite navigation, and so on. As a result, we need frequency synthesizer with higher comprehensive performance.Firstly, the direct digital synthesizer and phase-locked loop technologies are introduced an analyzed in this thesis. Though the frequency resolution and the speed of scanning speed of DDS is high enough, its output frequency, with a lot of spur,is low. In order to achieve better frequency synthesizer, we should use the technology of combining DDS and PLL. Among these several common phase-locked frequency synthesizers, the single loop which is feedback by frequency divider, can balance the frequency resolution with the phase noise and the output frequency bandwidth. And the single loop which is feedback by mixer, can solve the problem that when the output frequency is so high, the phase noise will be deteriorated badly, but at the sacrifice of the frequency resolution. Actually, multi-loop can solve all these problems, but its cost a lot, the structure is complex and power dissipation is high.So, in order to achieve a high performance synthesizer, this thesis have introduced a kind of new structure of phase-locked loop synthesizer, which has combined the DDS’s and the common phase-locked loops’ benefits. And in this project, the VCO is used, and the output frequency phase noise is as low as the YTO’s. This scheme has two key components,the one is the feedback circuit who’s phase noise is very low, and the other one is called reference frequency generator which is combined direct analog synthesis technology and DDS technology. The low phase noise feedback circuit is based on the mixer feedback structure, in this way, we can move out the divider, so that we can reduce the influence of phase noise, and at the same time, it’s will not decrease the frequency resolution. In the reference frequency generator, the direct analog synthesizer’s output frequency is used as DDS’s high stability external reference clock, then DDS generate high stability frequency with high resolution, and there is a circuit that can further reduce the signal’s phase noise and spurious level. At last, the new synthesizer can generate high stability frequency, and reached the desired design goals.